Conventional step transmissions are well known in the art using fixed ratio gearing which requires engine speed to increase in order to increase speed at the output. Except for changing gears, the transmission itself does not adjust to vary transmitted power. When used in motor vehicles, frequently any change in vehicle speed must result from a change in engine speed. Thus, the engine is frequently accelerated and decelerated, imposing considerable stress on the engine and drive train and increasing maintenance costs. Further, this changing of gears during operation of the vehicle requires that the drive be momentarily disconnected since power is transmitted exclusively through the single engaged gear pair.
Conventional transmissions further have an energy loss appearing as a heat pulse in the clutches when changing gears. For example, during vehicle acceleration, engine speed and thus vehicle speed are increased until a certain maximum engine speed is reached. At that point, a different gear pair is engaged which requires a lower engine speed to operate at that particular vehicle speed. Since the appropriate lower engine speed will seldom exist when the new gear pair is engaged, an energy loss resulting from a heat pulse occurs as the clutch slips until the appropriate engine speed exists. This heat pulse/energy loss is largest when the gear pairs are shifted with high torque on both gear shafts and thus must be considered in designing the gear pairs and clutch. The heat pulse can be limited by minimizing speed variations between gear pairs. This reduces the heat pulse but requires more gears and thus more shifting over a given range of vehicle speed. Consequently, heavy duty clutches which can handle large heat pulses are often necessary to hold down the number of gear pairs which must be used.
Infinitely variable transmissions already exist in several forms including belt and pulley, wheel on disc, interleaved discs, annular, double annular and nutating tubular types. These transmissions generally include a static torque reaction member. In addition, each receives power through a single path. Thus, although all may infinitely vary transmitted torque or speed within a range, the range itself may not be changed without disconnecting the drive. This results in the same drawbacks as are outlined above for conventional transmissions (i.e. heat pulse/energy loss occurring when gears are changed during high torque conditions, requiring higher cost clutches and gearing). Several varieties of these transmissions may avoid this problem by operating only within a single range so as to maintain drive at all times during operation. To transmit a desired wide range of power, these transmissions must be relatively bulky because component sizes must be increased. Similarly, such single range transmissions require that large normal forces be used to obtain sufficient traction forces, resulting in large component sizes due to design controlling stiffness and stress limitations.
The present invention is directed to overcoming one or more of the problems as set forth above.